Implantable medical leads and systems that utilize reflection points to control induced radio frequency energy

ABSTRACT

Implantable medical leads and systems utilize reflection points within the lead to control radio frequency current that has been induced onto one or more filars. The radio frequency current may be controlled by the reflection points to block at least some of the radio frequency current from reaching an electrode of the lead and to dissipate at least some of the radio frequency current as heat on the filar. Controlling the radio frequency current thereby reduces the amount that is dissipated into bodily tissue through one or more electrodes of the lead and reduces the likelihood of tissue damage. The reflection points may be created by physical changes such as to material or size in the filar and/or in insulation layers that may be present such as an inner jacket about the filar and an outer jacket formed by the body of the lead.

TECHNICAL FIELD

Embodiments are related to implantable medical leads and systemsincluding implantable medical leads that may carry induced radiofrequency energy. More particularly, embodiments are related toimplantable medical leads and related systems that include reflectionpoints to control the induced radio frequency energy.

BACKGROUND

Implantable medical systems include an implantable medical deviceconnected to an implantable medical lead. The implantable medical deviceis used to produce stimulation signals for delivery to tissue of apatient and/or to sense physiological signals from the tissue of thepatient. The implantable medical lead includes electrical contacts on aproximal end that are connected to electrical connectors within themedical device. Electrodes are present on a distal end of theimplantable medical lead to contact the tissue at the stimulation site.Filars are present within the lead to carry electrical signals betweenthe contacts at the proximal end and the electrodes at the distal end.

The implantable medical leads can present an issue for a patient who mayneed to undergo a magnetic resonance imaging (MRI) scan. An MRI scanexposes the patient to radio frequency (RF) electromagnetic energy. ThisRF energy may be collected by the filars in the form of induced RFelectrical current during the MRI scan. This RF electrical current maybe delivered to the tissue of the patient via the electrodes at thedistal end.

The RF electrical current induced onto the filars presents a seriouscondition. The electrode is a relatively small amount of surface areasuch that the RF electrical current from a given electrode is dissipatedinto a relatively small amount of tissue which may heat the tissue by anexcessive amount that causes tissue damage. Furthermore, the electrodemay be located adjacent to sensitive tissue such as within the brain orspine where tissue damage from the excessive heating by the induced RFcurrent may have severe consequences.

SUMMARY

Embodiments address issues such as these and others by providingimplantable medical leads and implantable medical systems where theimplantable medical leads include reflection points that control theradio frequency energy induced onto the filars. The reflection pointsmay be present on the filar(s) or on the insulation layer(s) such as onan inner jacket formed about individual liars or on an outer jacket ofthe lead. The reflection points may be created in various ways such aschanging physical dimensions like the diameter at a given point or bychanging the materials that are present at a given point

Embodiments provide implantable medical systems and leads. Theimplantable medical lead includes an outer jacket and a filar locatedwithin the outer jacket. The filar includes physical changes thatestablish multiple radio frequency reflection points located along thelength of the filar. The implantable medical lead further includes aproximal contact and a distal electrode, with the filar interconnectingthe proximal contact to the distal electrode.

Embodiments provide other implantable medical systems and leads. Theimplantable medical lead includes an outer jacket and a filar surroundedby an inner jacket. The filar and inner jacket are located within theouter jacket, and the inner jacket includes physical changes thatestablish multiple radio frequency reflection points located along thelength of the filar. The implantable medical lead further includes aproximal contact and a distal electrode, with the filar interconnectingthe proximal contact to the distal electrode.

Embodiments provide additional implantable medical systems and leads.The implantable medical lead includes an outer jacket and a filar beinglocated within the outer jacket such that the outer jacket includesphysical changes that establish multiple radio frequency reflectionpoints located along the length of the filar at non-standard intervalsof repetition. The implantable medical lead further includes a proximalcontact and a distal electrode, with the filar interconnecting theproximal contact to the distal electrode.

Embodiments provide other implantable medical systems and leads. Theimplantable medical lead includes an outer jacket and a filar beinglocated within the outer jacket. Discrete circuit elements areelectrically coupled to the filar and establish multiple radio frequencyreflection points located along the length of the filar at non-standardintervals of repetition. The implantable medical lead includes aproximal contact and a distal electrode, with the filar interconnectingthe proximal contact to the distal electrode.

DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a patient with an implantable medical system in thepresence of RF electromagnetic energy.

FIG. 2 shows an example of a longitudinal cross-section of animplantable medical lead having reflection points provided by changes infilar diameter, filar material, inner jacket diameter, inner jacketmaterial, outer jacket diameter, and outer jacket material.

FIG. 3 shows a first lateral cross-section of the implantable medicallead of FIG. 2 at a reference point.

FIG. 4 shows a second lateral cross-section of the implantable medicallead of FIG. 2 at a first reflection point.

FIG. 5 shows a third lateral cross-section of the implantable medicallead of FIG. 2 at a second reflection point.

FIG. 6 shows a fourth lateral cross-section of the implantable medicallead of FIG. 2 at a third reflection point.

FIG. 7 shows a fifth lateral cross-section of the implantable medicallead of FIG. 2 at a fourth reflection point.

FIG. 8 shows a sixth lateral cross-section of the implantable medicallead of FIG. 2 at a fifth reflection point.

FIG. 9 shows a seventh lateral cross-section of the implantable medicallead of FIG. 2 at a sixth reflection point.

FIG. 10 shows an eighth lateral cross-section of the implantable medicallead of FIG. 2 at a seventh reflection point.

FIG. 11 shows a ninth lateral cross-section of the implantable medicallead of FIG. 2 at an eighth reflection point.

FIG. 12 shows a tenth lateral cross-section of the implantable medicallead of FIG. 2 at a ninth reflection point.

FIG. 13 shows an eleventh lateral cross-section of the implantablemedical lead of FIG. 2 at a tenth reflection point.

FIG. 14 shows a longitudinal distribution of reflection points in oneexample of a lead.

DETAILED DESCRIPTION

Embodiments provide implantable medical leads and systems that includereflection points along the leads to control RE energy that is inducedas RE current onto filars of the leads. The reflection points may bepresent on the filar or on other elements of the lead such as an innerjacket around the individual filar or an outer jacket that may form theouter body of the lead. The reflection points may be created by physicalchanges such as a change in diameter of the filar or insulator or achange in the materials that are used for the filar or insulator thatproduce a change in a characteristic impedance of the lead.

FIG. 1 shows an environment where an implantable medical system 100 hasbeen implanted within a patient 108. The implantable medical system 100includes an implantable medical device (IMD) 102 and an implantablemedical lead 104. The implantable medical lead 104 is connected to theIMD 102 at a proximal end, and the lead 104 extends to a stimulationsite where electrodes 106 on the distal end are present to electricallyinterface with the tissue of the patient 108.

The patient 108 is being exposed to RE electromagnetic energy 110. ThisRE energy 110 encounters the implantable medical system 100 and mayinduce RF current onto the lead 106. However, the lead 106 may includereflection points positioned at various locations to reflect the RFcurrent away from the electrodes and to cause at least some of the REcurrent to dissipate as heat over the filar(s) present within the lead104 rather than exiting through the electrodes 106.

FIG. 2 shows a longitudinal cross-section of an example of a lead 200with reflection points. This lead 200 is shown with a single contact204, single filar 208, and single electrode 206. It will be appreciatedthat any number of contacts, filars, and electrodes may be present andmay benefit from the reflection points. In this particular example, thelead 200 includes a body 202 which may be established by the outerjacket, or the outer jacket may be an outer layer adhered to the body202. The body 202 defines a lumen 210 that may be present to receive astylet that guides the lead 200 during implantation and is removedthereafter.

The body 202 forming the outer jacket may be made of various materials.Examples include elasthane, silicone, other polymers and the like.Likewise, the filar 208 may be made of various materials such as MP35N®alloy, platinum, silver cored MP35N® alloy, and the like.

Additionally, the lead 200 may include an inner jacket that is not shownin FIG. 2 but adheres to the outer surface of the filar 204 and isolatesthe filar 204 from the body 202. The inner jacket may also be made ofvarious materials. Examples include ethylene tetrafluoroethylene (ETFE),other polymers, and the like.

The physical parameters including the dimensions and the types ofmaterial used for each of the components within the lead 200 such as theouter jacket of the body 202, the inner jacket, and the filar 206contribute to the characteristic impedance of the filar 202. To create areflection point, the characteristic impedance is altered at a givenlocation where the reflection point is desired. To alter thecharacteristic impedance and thereby create the reflection point, aphysical change is present in either a dimension or a material for theparticular component. Examples of such physical changes are present inthis example of the lead 200, where cross-section 3-3 shown in FIG. 3 isa reference point showing the normal construction where a reflectionpoint is not present. Cross-sections 4-4 through 13-13 show examples ofsome of the other reflection points that are present in this example ofthe lead 200.

FIG. 3 shows a lateral cross-section taken through 3-3 of FIG. 2. Here,the elements of the lead 200 including the body 202 forming the outerjacket, the filar 212, and the inner jacket 208 on the filar 212 arenormal in that this represents the configuration of the areas of thelead where no reflection point is present. In the example of FIG. 2,this cross-section taken through 3-3 is in a normal portion near theproximal end of the lead 200. It will be appreciated that normalportions such as this that may extend for significant portions of thelead may appear at any point along the lead from proximal tip to distaltip.

FIG. 4 shows a lateral cross-section taken through 4-4 of FIG. 2 where areflection point is present. Here, the body 202 forming the outer jacketincludes additional material 202′ creating a larger diameter over aparticular length of the lead 200. The additional material 202′ may bethe same or different material than the body 202. The other elementsincluding the filar 212 and inner jacket 214 have not changed. Thechange in diameter results in a change to the characteristic impedanceof the filar 202 thereby producing a reflection point. It will beappreciated that rather than increasing the diameter, the body 202forming the outer jacket may have a reduced diameter to create areflection point.

An alternative to the layer 202′ being an additional jacket material,202′ may represent a floating electrode. In this case, the floatingelectrode may be attached to the body 202 in the same manner as theelectrode 206 that is used for stimulation, but the floating electrodeis not connected to a filar 212. The floating electrode presents aphysical change to the outer jacket that creates a change in thecharacteristic impedance of the filar 212 such that the presence of thefloating electrode creates a reflection point. In some examples, thefloating electrode present at any given reflection point may becapacitively coupled to one or more of the filars within the lead 200.

FIG. 5 shows a lateral cross-section taken through 5-5 of FIG. 2 where areflection point is present. Here, the body 202 forming the outer jacketincludes one or more types of dopant materials. In this particularexample, two dopant materials 216 and 218 are present and create achange in the conductance of the outer jacket over a particular lengthof the lead 200. Examples of dopant materials include metals such astitanium, stainless steel, platinum, and the like. The other elementsincluding the filar 212 and inner jacket 214 have not changed. Thechange in material results in a change to the characteristic impedanceof the filar 202 thereby producing a reflection point.

FIG. 6 shows a lateral cross-section taken through 6-6 of FIG. 2 where areflection point is present. Here, the body 202 forming the outer jacketis normal in size and material. However, the inner jacket 214 includesadditional material 214′ creating a larger diameter over a particularlength of the lead 200. The additional material 214′ may be the same ordifferent material than the material of the inner jacket 214. The otherelements including the filar 212. and body 202 forming the outer jackethave not changed. The change in diameter results in a change to thecharacteristic impedance of the filar 202 thereby producing a reflectionpoint. It will be appreciated that rather than increasing the diameter,the inner jacket 214′ may have a reduced diameter to create a reflectionpoint.

FIG. 7 shows a lateral cross-section taken through 7-7 of FIG. 2 where areflection point is present. Here, the body 202 forming the outer jacketis normal in size and material. However, the inner jacket 214′ includesat least one type of dopant material. In this particular example, twodopant materials 220 and 222 are present and create a change in theconductance of the outer jacket over a particular length of the lead200. Examples of these dopant materials also include titanium, stainlesssteel, platinum, and the like. The other elements including the filar212 and body 202 forming the outer jacket have not changed. The changein materials results in a change to the characteristic impedance of thefilar 202 thereby producing a reflection point.

FIG. 8 shows a lateral cross-section taken through 8-8 of FIG. 2 where areflection point is present. Here, both the body 202 forming the outerjacket and the inner jacket 214 are normal in diameter and material.However, the filar 212′ has a reduced diameter, such as by creating acrimp and the inner jacket 214 may fill in the area of reduced diameter.The change in diameter of the filar 212′ at the area of thiscross-section results in a change to the characteristic impedance of thefilar 202 thereby producing a reflection point. It will be appreciatedthat rather than reducing the diameter, the filar 212′ may have anincreased diameter to create a reflection point such as by weldingadditional material onto the filar 212′.

FIG. 9 shows a lateral cross-section taken through 9-9 of FIG. 2 where areflection point is present. Here, both the body 202 forming the outerjacket and the inner jacket 214 are normal in diameter and material.However, the filar 212 has a change in material by the addition of amaterial 212″ adjacent to the material 212, such as by welding adifferent material 212″ onto the existing filar 212. It should be notedthat both materials define the surface, which may provide a moreeffective reflection point than using an approach with a coreconsidering that the RE induced current is primarily on the surface dueto the skin effect. If the filar diameter is to be maintained as shownin FIG. 9, the existing filar material may have a reduced filar diameterwhile the new filar material increases the filar diameter back to thenormal level. The change in material of the filar 212″ at the area ofthis cross-section results in a change to the characteristic impedanceof the filar 202 thereby producing a reflection point.

FIGS. 4-9 have shown examples where a single parameter such as size ormaterial has changed to produce a reflection point. FIGS. 10-13 showexamples where multiple parameters have changed to produce for each ofthe reflection points.

FIG. 10 shows a lateral cross-section taken through 10-10 of FIG. 2where a reflection point is present. Here, the inner jacket 214 isnormal in diameter and material. However, the filar 212″ has a change inmaterial while the diameter may be the same or different, such as bywelding a different material onto the existing filar 212. Additionally,the body 202 forming the outer jacket has additional material 202′ thatincreases the diameter of the body 202. The combination of the change inmaterial of the filar 212″ as well as the diameter of the outer jacket202′ at the area of this cross-section results in a change to thecharacteristic impedance of the filar 202 thereby producing a reflectionpoint. It will be appreciated that the multiple parameters relating tothe filar 212 and the body 202 forming the outer jacket may haveadditionally or alternatively included other changes such as a reduceddiameter of the body 202′ forming the outer jacket, a change to thediameter of the filar 212, and/or a change to the material of the body202, 202′ forming the outer jacket.

FIG. 11 shows a lateral cross-section taken through 11-11 of FIG. 2where a reflection point is present. Here, the body 202 forming theouter jacket includes one or more types of dopant materials. In thisparticular example, one dopant material 216 is present. Additionally,the inner jacket 214 includes additional material 214′ increasing thediameter of the inner jacket. The combination of the change in materialof the body 202 forming the outer jacket and the change in diameter ofthe inner jacket 214 results in a change to the characteristic impedanceof the filar 202 thereby producing a reflection point. It will beappreciated that the multiple parameters relating to the body 202forming the outer jacket and the inner jacket may have additionally oralternatively included other changes such as a change in diameter of thebody 202 forming the outer jacket, a reduced diameter of the innerjacket 214, and/or a change in the material of the inner jacket 214.

FIG. 12 shows a lateral cross-section taken through 12-12 of FIG. 2where a reflection point is present. Here, the inner jacket 214″includes one or more dopant materials. In this particular example, onedopant material 220 is present. Additionally, the filar 212′ has areduced diameter. The combination of the change in material of the innerjacket 214″ and the change in diameter of the filar 212′ results in achange to the characteristic impedance of the filar 202 therebyproducing a reflection point. It will be appreciated that the multipleparameters relating to the inner jacket and filar may have additionallyor alternatively included other changes such as a change in diameter ofthe inner jacket 214″, a change in diameter of the inner jacket 214″,and/or a change in the material of the inner jacket 214.

FIG. 13 shows a lateral cross-section taken through 13-13 of FIG. 2where a reflection point is present. Here, the inner jacket 214″includes one or more dopant materials. In this particular example, onedopant material 222 is present. The inner jacket 214″ also includesadditional material 214′ increasing the diameter of the inner jacket,Additionally, the filar 212′ has a reduced diameter while also includinga different material 212″ welded onto the existing reduced diameterportion 212′. The body 202 forming the outer jacket includes additionalmaterial 202″ that increases the diameter of the body 202 forming theouter jacket. Furthermore, the additional material 202″ is doped withone or more dopants, in this case a single dopant type 218. Thecombination of the change in materials and sizes of the inner jacket214′, 214″, the filar 212′, 212″, and the body 202, 202″ forming theouter jacket result in a change to the characteristic impedance of thefilar 202 thereby producing a reflection point. it will be appreciatedthat the multiple parameters relating to the body forming the outerjacket, the inner jacket and the filar may have additionally oralternatively included other changes as well.

FIG. 14 shows an example of longitudinal distribution 300 of reflectionpoints 302 along the length of a lead. It can be seen that somereflection points are created by a change only to a single element, theouter jacket (1), the inner jacket (2), or the filar (3). It can be seenthat some reflection points are created by a change to two elements, theouter jacket (1) and the inner jacket (2), the outer jacket (1) and thefilar (3), or the inner jacket (2) and the filar (3). Additionally, itcan be seen that some reflection points are created by a change to allthree elements, the outer jacket (1), the inner jacket (2), and thefilar (3).

In FIG. 14 it can further be seen that in this example there is anonstandard interval of repetition. In other words, the spacing from onereflection point to the next reflection point varies. It can also beseen in this example that there is a nonstandard interval of repetitionfrom a reflection point involving a change to a particular element tothe next reflection point involving the same element. This nonstandardinterval of repetition may assist in reflecting the RF current away fromthe electrode and in dissipating the RF current as heat in the filar(s).

While the examples of FIGS. 2-13 show a single filar and a single innerjacket, multiple filars may be present and each filar may have adedicated inner jacket. The physical change to the filar and/or theinner jacket may vary from filar to filar. For instance, a givenreflection point involving the inner jacket (2) and/or the filar (3) asshown in FIG. 14 may pertain to one filar, multiple filars, or allfilars present within a lead. For instance, some of those reflectionpoints of FIG. 14 may pertain to one filar while others may pertain tomultiple filars.

The reflection points discussed herein may also be created by thepresence of discrete circuit elements such as resistors, capacitors,and/or inductors that are electrically coupled to the filar(s). Thus,any or all of the reflection points 302 illustrated in FIG. 14 may bediscrete circuit elements with nonstandard intervals of repetitionrather than physical changes to the filar, inner jacket, or outerjacket. For instance, there may be series resistors in-line along thefilars (1), series inductors in-line along the filars (2), and/orcapacitors that are parallel from the filar to floating electrodes thatmay have a large surface area in comparison to the stimulationelectrodes and/or may be located in less critical tissue (3) that arepresent to vary the characteristic impedance while not adverselyaffecting the delivery of stimulation signals or sensed signals throughthe filars.

While embodiments have been particularly shown and described, it will beunderstood by those skilled in the art that various other changes in theform and details may be made therein without departing from the spiritand scope of the invention.

1. An implantable medical system, comprising: an implantable medicaldevice; and an implantable medical lead connected to the implantablemedical device, the implantable medical lead comprising: an outerjacket; a filar surrounded by an inner jacket, the filar and innerjacket being located within the outer jacket, the inner jacket includingphysical changes that establish multiple radio frequency reflectionpoints located along the length of the filar; a proximal contact; and adistal electrode, the filar interconnecting the proximal contact to thedistal electrode.
 2. The implantable medical system of claim 1, whereinthe physical changes occur at non-standard intervals of repetition. 3.The implantable medical system of claim 1, wherein the physical changecomprises a change in inner jacket diameter.
 4. The implantable medicalsystem of claim 1, wherein the change in inner jacket diameter comprisesan increase in inner jacket diameter.
 5. The implantable medical systemof claim 1, wherein the physical change comprises a change in a type ofinner jacket material.
 6. The implantable medical system of claim 5,wherein the change in the type of material comprises a doped innerjacket material adjacent to an existing inner jacket material.
 7. Theimplantable medical system of claim 6, wherein the doped inner jacketmaterial comprises multiple dopants.
 8. The implantable medical systemof claim 1, wherein the filar includes physical changes that establishmultiple radio frequency reflection points located along the length ofthe filar.
 9. The implantable medical system of claim 1, wherein theouter jacket includes physical changes that establish multiple radiofrequency reflection points located along the length of the filar. 10.An implantable medical system, comprising: an implantable medicaldevice; and an implantable medical lead connected to the implantablemedical device, the implantable medical lead comprising: an outerjacket; a filar being located within the outer jacket such that theouter jacket includes physical changes that establish multiple radiofrequency reflection points located along the length of the filar atnon-standard intervals of repetition; a proximal contact; and a distalelectrode, the filar interconnecting the proximal contact to the distalelectrode.
 11. The implantable medical system of claim 10, wherein thephysical change comprises a change in outer jacket diameter.
 12. Theimplantable medical system of claim 10, wherein the change in outerjacket diameter comprises an increase in outer jacket diameter.
 13. Theimplantable medical system of claim 10, wherein the physical changecomprises a change in a type of outer jacket material.
 14. Theimplantable medical system of claim 13, wherein the change in the typeof material comprises a doped outer jacket material adjacent to anexisting outer jacket material.
 15. The implantable medical system ofclaim 14, wherein the doped outer jacket material comprises multipledopants.
 16. The implantable medical system of claim 10, wherein thefilar includes physical changes that establish multiple radio frequencyreflection points located along the length of the filar.
 17. Theimplantable medical system of claim 10, wherein the filar is surroundedby an inner jacket, the inner jacket being located within the outerjacket, the inner jacket including physical changes that establishmultiple radio frequency reflection points located along the length ofthe filar.
 18. An implantable medical system, comprising: an implantablemedical device; and an implantable medical lead connected to theimplantable medical device, the implantable medical lead comprising: anouter jacket; a filar being located within the outer jacket, the filarincluding physical changes at non-standard interval of repetition thatestablish additional radio frequency reflection points along the lengthof the filar; discrete circuit elements electrically coupled to thefilar that establish multiple radio frequency reflection points locatedalong the length of the filar at non-standard intervals of repetition; aproximal contact; and a distal electrode, the filar interconnecting theproximal contact to the distal electrode.